The production of sintered parts from "green" bodies is well known in the art. Generally, the green body is formed by filling a die with a powder/binder mixture and compacting the mixture under pressure to produce the green body. The green body, a self-supporting structure, is then removed from the die and sintered. During the sintering process, the binder is volatilized and burned out.
Heretofore, aqueous compositions useful as injection molding precursors have been prepared using batch-type processes. For example, U.S. Pat. No. 4,734,237 discloses the preparation of aqueous ceramic injection molding compounds using a sigma blender for blending the precursor liquid and powder ingredients. U.S. Pat. No. 5,250,251 gives examples of aqueous compositions prepared using a batch sigma mixer for molding articles from aluminum oxide, zirconium oxide and silicon nitride. Similarly, in U.S. Pat. No. 5,087,595 a batch mixer was used to prepare yttrium oxide/zirconium oxide molding compounds for fabricating oxygen sensors. Injection molding compounds containing metal powder are disclosed in U.S. Pat. No. 5,258,155, wherein the metal powder is kneaded with binder, water and other additives in a batch mixer. Aqueous injection molding compositions containing metal powder are disclosed in U.S. Pat. No. 4,113,480, wherein the binder and metal powder are pre-blended dry and then mixed with a solution of water and additives.
It is widely recognized that the quality of the green and fired metal or ceramic body is largely dependent upon the uniformity of the precursor molding feedstock composition, and that batch-to-batch variations in the feedstock produced can have a marked effect on the properties of molded objects made from such feedstock materials.